Polarizing glasses having integral non-polarizing regions

ABSTRACT

Polarizing glass having localized regions or patterns of non-polarizing glass is disclosed. The glass is formed by use of reducing gas-blocking material, by local thermal heating of the glass, or by an etching technique.

CROSS-REFERENCED APPLICATIONS

The present application is a divisional application of U.S. Ser. No.09/142,962 filed on May 21, 1999, which is now U.S. Pat. No. 6,171,762,granted Jan. 9, 2001, by Nicholas F. Borrelli, Chad B. Moore and Paul A.Sachenik, which, is a 317 of PCT/US97/04870 filed Mar. 25, 1997, whichin turn, claims priority of the Provisional Application Serial No.60/014,619 filed on Mar. 28, 1996.

BACKGROUND OF THE INVENTION

Hydrogen firing at elevated temperatures to change the color of glasseswhose compositions contain reducible ions is well known. A notablecommercial application of that technique is found in the CorningIncorporated eyewear product lines marketed under the SERENGETI® andCPF® trademarks. The color changes induced are attributed, to thereduction of a portion of the silver and lead ions respectively, in theglass to the atomic state.

Several methods have been suggested for making polaizing glasses. Forexample, one such method is to redraw a glass above its softeningtemperature. The glass contains a separate phase which is elongated bythe redraw process. The thermal treatment which leads to the phaseseparation is usually carried out before the redraw process. In aparticular version of the above process, the separated phase isinitially spectrally non-absorbing material such as AgClBr, CuCIBr, AgI,CuI or copper/cadmium halides, which must be subsequently modified tocreate a desired dichroic property necessary for the polarizing effect.This is accomplished by treating the stretched glass in hydrogen gas atelevated temperatures for sufficient time to effect the chemicalreduction of the spectrally non-absorbing materials to theircorresponding metal. The chemical reduction process is a combinedprocess involving both the diffusion of hydrogen in the glass, and thechemical reaction of the hydrogen with the halide phase.

It is known that the chemical reaction proceeds very fast relative tothe hydrogen diffusion which leads to the condition of a sharp boundarybetween the reduced region near the surface, and the unreduced regionbelow the surface. The polarizing behaviors derives from the reducedlayer. Also, when the polarizing glass is heated to the vicinity of 500°C. for any prolonged period of time, the elongated particlesre-spheridize and the polarizing property is lost. That is, theelongated particle returns to its spherical shape. This is explained bythe fact that once the glass is soft enough, the interfacial forces actto undo what the redrawing forces had accomplished.

For certain applications, it is desirable to have the polarizingproperties restricted to localized regions of the glass. Accordingly, itis the object of the present invention to provide methods of partiallyor fully blocking the effect of hydrogen reduction over a portion of aglass surface, or other ways of altering the polarizing state.

SUMMARY OF THE INVENTION

Briefly, the invention relates to a polarizing glass having an integralnon-polarizing region.

In one aspect, the invention relates to a method of producing apolarizing glass in which a region on the glass surface is renderednon-polarizing.

In a particular aspect, the invention relates to a method of forming aglass having integral polarizing and non-polarizing regions by:

(a) providing a glass having an elongated (stretched) reducible phase;

(b) protecting or masking a portion of the glass by selectively forminga layer of material on the surface of said portion of the glass;

(c) subjecting the unprotected regions of the glass to a reducing gas toreduce the reducible phase in said region; and

(d) removing the layer of material from the protected portion to revealthe underlying non-polarizing glass to thereby form a glass havingintegral polarizing and non-polarizing regions.

In still another aspect, the invention relates to a method of forming anon-polarizing region in a polarizing glass by, providing a polarizingglass comprising reducible elongated phase particles; and thensubjecting a region of the glass surface to thermal heating tore-spheridize the elongated phase and thereby render the polarizingglass, non-polarizing in said region.

In yet another aspect, the invention relates to a method of forming anon-polarizing region in a polarizing glass by selectively removing thepolarizing layer to render the glass in said region, non-polarizing.

As used herein:

“reducing atmosphere” refers to a gaseous atmosphere in which thechemical potential of oxygen is low. Examples of reducing gases includehydrogen, hydrazine vapor, cracked ammonia, deuterium and forming gas(i.e., a mixture of hydrogen and an inert gas, for example, H₂/He andH₂/N₂).

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a to 1 c are schematic diagrams illustrating one inventive methodof forming a polarizing glass having at least one non-polarizing region;

FIGS. 2a to 2 d are schematic diagrams illustrating another inventivemethod of forming a pattern of polarizing and non-polarizing glass, by aphotolithographic process;

FIGS. 3a and 3 b are schematic diagrams illustrating an embodiment ofthe invention, involving, exposing an assembly of polarizing glass andphotoresist to light radiation, developing the photoresist to expose theunderlying polarizing layer (FIG. 3a), etching the exposed region toremove the polarizing layer in said region, and the stripping away thephotoresist (FIG. 3b).

DETAILED DESCRIPTION OF THE INVENTION

We have found, and disclose herein, that a polarizing glass havingnon-polarizing regions can be formed by (1) use of a hydrogen blockingfilm, (2) local thermal treatment, (3) etching, or (4) a combination ofthese methods. For ease of discussion, the layer of educing gas blockingmaterial will be referred to herein as “hydrogen-blocking film” eventhough it is understood that in addition to hydrogen, other reducinggases such as cracked ammonia, deuterium or forming gas (i.e., a mixtureof H₂ with He, N₂, or Ar) may be used.

As contemplated by the present methods, the polarizing glass contains areducible elongated phase such as, AgCl_(x)Br_(1-x), CuCl_(x)Br_(1-x),where x has a value between 0 and 1, or phase separated Pb-borate glass.Other useful reducible phases include, AgI, CuI and Cu/Cd halides.

The invention will now be described with reference to the drawings. Inthe hydrogen blocking method (FIGS. 1a to 1 c), a thin layer of material6, preferably a dense film of material such as Cr, Mo or their oxides isformed on the surface of a non-polarizing glass 2 to retard thereduction process and enable the production of color gradients anddesigns or patterns on the glass. In a particularly useful embodimentusing this technique, a non-polarizing region 10 is formed in a glasshaving a stretched or elongated particles by using a reducing gas and apatterned film which is capable of retarding penetration of the reducinggas. In this embodiment, the non-polarizing region is formed by:

1) providing a glass 2 having a layer of reducible elongated phase;

2) protecting a region of the glass by forming a layer of blockingmaterial 6 on the surface of the region of the glass to be protected,the material being capable of blocking or preventing penetration of areducing gas (FIG. 1b);

3) subjecting the unprotected region 8 of the glass to a reducing gasatmosphere to reduce the reducible phase in the unprotected region 8 andthereby render said region polarizing; and

4) removing the layer of blocking material 6 from the protected regionto reveal the underlying non-polarizing glass (FIG. 1c).

The preferred reducing gas can be H₂, cracked ammonia, forming gas andD₂. If forming gas is used, then the hydrogen content of the forming gasmixture is preferably at least 0.1%, more preferably, at least 5%, andmost preferably, at least 10%. The higher the hydrogen content of theforming gas mixture, the lower the pressure and the less the timerequired to reduce the reducible phase in the glass. The preferredforming gas is H₂/N₂.

The layer of hydrogen-blocking material may be patterned using anymethod. A particularly useful method of selectively forming the thinfilm layer is by placing a shadow mask 4 above the glass surface, suchthat the mask shadows or protects certain regions of the glass (FIG. 1).A patterned layer of blocking material is thereby formed on the unmaskedor unprotected regions of the glass through holes or openings in theshadow mask.

Another useful method of patterning the thin film blocking layer is byusing photolithography (FIG. 2). In this patterning process, (i) a thinfilm of hydrogen-blocking material 6 is deposited over the entiresurface of a reducible glass 2, that is, a glass having a layer ofstretched or elongated particles; (ii) a thin photoresist layer 12 isthen applied to the surface of the hydrogen-blocking material 6 (FIG.2a); (iii) the photoresist is lithographically patterned using a maskand developed (FIG. 2b); (iv) the patterned photoresist image is thentransferred into the layer of blocking material by an etching process(dry or wet); and (5) the photoresist is removed leaving a patternedfilm blocking material (FIG. 2c). To form a region of non-polarizingglass, the assembly of FIG. 2c is exposed to a reducing gas atmosphereas above to render the glass polarizing in the unprotected region. Thenthe blocking material is removed to form a glass having polarizing 8 andnon-polarizing 10 regions as shown in FIG. 2d.

We have found that the particular method used to deposit the thin layerof material is a key aspect of the invention. In particular, to avoidthe formation of pinholes in the layer, the film is deposited,preferably in a Class 1000 (or better) clean room environment, bysputtering or other suitable methods.

The choice of the blocking material and its deposited thickness is madeon the basis of how deep a reduced layer in the glass is required forany given application. In other words, the property of the depositedfilm, through the combined property of density and thickness, must besufficient to retard the diffusion of H₂ for thetime/pressure/temperature required to produce a sufficient reduced depthin the glass, in turn, providing the desired contrast For example, thedepth to which the silver or copper halide phase is chemically reducedto silver, or copper (i.e., the thickness of the polarizable layer),determines the contrast of the polarizer. It has been shown that thereduced depth is proportional to the square root of the H₂ pressure andthe time of treatment, as well as an exponential function of thetemperature.

The contrast is defined as the ratio of the transmittance in the passingdirection (perpendicular to the stretched direction, T₀) to thetransmittance in the absorbing direction (parallel to the stretchingdirection). One can mathematically express this in terms of thethickness of the polarizing layer by the equation, contrast=T₀/exp(−αd)where d is the polarizing film thickness. The coefficient, α, depends onthe wavelength of light and the degree to which the glass was stretched.For a given application, α, and T₀ are determined experimentally, andthe thickness of the polarizing film can be determined for any desiredcontrast. In one particularly useful embodiment, at a wavelength of 640nm, a thickness of 28 μm is required to achieve a contrast of 100.

The particular choice of a material for use in the blocking of hydrogen,such as, Cr, Mo, Ta, Zn, W, may depend on the method used to form thethin layer and the related deposition variables. Other useful hydrogenblocking materials include the noble metals such as Au, Rh, Pd, Pt, andIr. For example, where the layer is formed by film deposition method,the relevant variables may include the porosity of the deposited film,which depends on the specific deposition method and system, the filmadherence, and how it varies with thickness, the thermal mismatch, andhow it relates to thickness. These latter issues relate to the qualityof the film that is produced, pinholes, cracks, and other features thatwould allow H₂ to penetrate through the film. A summary of illustrativeresults using several hydrogen blocking materials films is shown inTable 1. For this particular case the high contrast was desired at awavelength of 640 nm.

In another embodiment, localized heating is used to render a portion ofa polarizing glass, non-polarizing. In the local heating method, anon-polarizing region is formed in a polarizing glass by subjecting aregion of the glass surface to thermal heating to re-spheridize theelongated phase and thereby render the polarizing glass, non-polarizingin the region of thermal contact. The object is to locally heat theglass to above about 450° C., preferably, above about 500° C. in amanner appropriate for forming the desired pattern. In the heatedregion, the elongated phase will be re-spheroidized and renderednonpolarizing. An important point to realize is that one need only toheat the relatively thin surface polarizing layer to above 450° C.,which means the amount of heat required can be quite small. This can beachieved by a number of ways. One way to easily localize the heatedregions is to use a light source, such as laser, at a wavelength wherethe effective absorption depth, usually defined as the reciprocal of theabsorption coefficient, is approximately equal to the polarizing filmthickness. In this way the light is primarily absorbed in the layer tobe heated. In this embodiment, care must be taken to avoid possibleoverheating, and the physical damage that may result from suchoverheating. The power input must be sufficiently controlled to maintaina safe temperature and avoid any possible damage.

An example of a light source that satisfies the above stated conditionsis a CO₂ laser. The intensity distribution of the beam is important inthat it will influence the temperature profile and, therefore, affectthe nature of the transition from the non-polarizing to polarizingregion. One can influence this by using a mask in a scanning mode, or amultimode laser with a flat intensity profile. In one embodiment, a CO₂laser source is focused on a region of polarizing glass to heat theglass in said region and thereby render the glass non-polarizing byre-spheroidizing the elongated phases as described above.

Another way to provide local heating is to use a polarized light sourcewhose polarization direction is oriented in the absorbing orientation ofthe polarizing material. The wavelength of the light is chosen tocorrespond to the high contrast spectral region.

Another way to provide local heating in the thin polarizing layer is touse a high current of an energetic beam, such a electrons or ions,either focused or in conjunction with a suitable mask. The beam wouldlocally heat the polarized surface layer.

Another useful method of forming a non-polarizing region by localthermal treatment, is by thermal contact. In one such embodiment, heatedtips or ridges are brought in contact with the polarized layer of theglass to heat the contact region, and thereby effect re-spheroidization.

In using the thermal contact method, care must be taken to avoid thermalshock which may result due to the rapid heating and cooling. Onepossible disadvantage of the thermal heating methods is the residualbirefringence that may result from the rapid heating and cooling. Thiscan be mitigated by careful annealing. In this embodiment, it is notnecessary to directly contact the polarizing glass with the heat source,as effective heating can be achieved without direct contact. Thus, itmay be sufficient to bring the heat source to the proximate region ofthe glass to be heated, since it is the heat radiation, rather than theheat source itself that is required to achieve the objective of thismethod.

The etching method (FIGS. 3a and 3 b), relies on the selective removalof the polarizing layer by any number of etching techniques. In thismethod, parts of the polarizing layer 8, is protected by use of a filmor layer of metal or photoresist 16. The unprotected layer of polarizingglass is then etched to remove the polarizing layer and thereby form apolarizing glass having an integral non-polarizing region 20 (FIG. 3b).The protected region restricts the removal of the polarized surfacelayer. Preferably, the thickness of the polarizing layer is in the rangeof 10-50 microns, depending on the polarizing property required. Theselective removal or etching away of the polarizing layer may be done byeither wet or dry etching techniques. This method may produce a phasefront alteration to a beam because light passing through it may havedifferent optical paths in the etched and non-etched areas. This frontalteration may be undesirable for certain applications.

EXAMPLES

1. Hydrogen Blocking

a) A Mo film of the order of 1 μm thick was deposited through apatterned shadow mask onto a stretched glass surface. The mask wasmaintained in intimate contact with the sample. The metal patternedsample was then treated in pure H₂ atmosphere at 420° C., 1 atm, for 17hours. A polarizing layer having a depth of about 30 μm was formed inthe unmasked region, while the masked region remained non-polarizing.The Mo film was then removed by a suitable acid. If a single sidedpatterned polarizing effect is desired, the entire back side can becovered with Mo to protect it. If desired, a two-sided product may beproduced by apply the same or a different pattern on the opposite sideof the glass. In this example, the hydrogen-blocking material wasapplied by sputtering, in a Class 1000 clean room environment.

b) Same as above except that the hydrogen-blocking material was Cr,having a thickness of about 0.6 μm. The H₂ treatment was at 420 ° C., at1 atm, for 3 hours. The resulting polarizing layer had a depth of about15 μm.

c) Same as above except that the hydrogen-blocking layer was 1 μm ofZnO. The H₂ treatment was 420° C. for 3 hours, at 1 atm. Thickness ofthe polarizing layer was 15 μm

In a similar experiment, we found that Mo film having a thickness as lowas 0.5 μm can be treated in a hydrogen environment at 1 atm, 420° C. for16 hours without any bleed through. That is, the hydrogen did notpenetrate through the Mo film into the underlying glass. We have foundthat the higher the pressure, the more likely the hydrogen is to bleedthrough the film. Also, the denser the film the less likely the hydrogenis to bleed through the film. For a given hydrogen-blocking material,the optimal reducing gas treatment conditions (time, temperature,pressure) necessary to minimize or reduce bleed through can bedetermined by experimentation. For example, if a forming gas mixturehaving low hydrogen content is used, then the reducing gas treatment canbe carried out at high pressure with minimal effect from any resultingbleed through.

2. Local Heating

a) A glass sample having a reducible elongated phase was exposed to ahydrogen environment as described above to form a polarized glass. A 4Wcw CO₂ laser was focused to a 1.5 mm spot on the polarized glass samplefor a fraction of a second using a shutter. The exposed spot was yellowin color, and non-polarizing corresponding to the condition of therespheroidization of the elongated silver particles.

b) The same as above, but the sample was exposed to the CO₂ laser beforethe H₂ treatment. This heat treatment respheroidized the metal halideparticle in the region exposed to the laser. The sample was then treatedin a H₂ atmosphere as described above to develop the polarizing layer.Because the heated area only contained spherical particles, nopolarizing property was developed in the exposed area.

3. Etching

a) A glass sample having a stretched or elongated layer was coated with0.2 μm of Cr and then coated with photoresist. The sample was exposed tolight through a mask containing the desired pattern as shown in FIG. 2.The resist was then developed to expose the underlying Cr layer in theunmasked region, and the Cr layer was etched away. The remainingphotoresist material was then stripped leaving a pattern ofmetal-covered and uncovered regions, (FIG. 3a). Using a wet chemicaletching technique, the sample was then dipped in dilute HF for asufficient time to dissolve the glass in the uncoated region to athickness corresponding to the polarizing layer. The Cr layer was thenstripped to obtain a polarizing glass, having an integral non-polarizingregion, (FIG. 3b).

b) The same as above, except that a dry etching process (reactive ionetching) was used to remove the polarizing glass layer at a rate ofabout 3 μm per hour.

The Preferred Embodiment

In the preferred embodiment, the metal films used to inhibit the H₂penetration were delineated using a shadow mask. Samples were preparedusing two dense metal—Cr and Mo. Thin layers of the hydrogen-blockingmetal were deposited using either a CVC DC sputtering system or a MRCin-line sputter system, both in a Class 1000 clean room. If desired, afilm of the reducing gas blocking material may also be applied to theother surface to the polarizing glass prior to the hydrogen treatment.The deposition conditions were as

Cr Mo Pressure (mT) 1 10 Power (W) 1000 1000 Deposition Rate (A/s) 3.515 Rotation number 5.0 Belt speed (in/min) 10 Passes 6

The glass used in all cases was Polarcor™ (available from CorningIncorporated), with a 680 nm center peak wavelength. The samples wereground and polished to a thickness of 0.5 mm before hydrogen treatment.The results are summarized in the table below.

TABLE 1 Thickness H₂- of H₂ block. H₂ treatment Polarizing film block.material Temp/time/pressure Thickness Mat'l (μm) (° C./hours/atm) (μm)Cr 0.4-0.6 415/3/1 15 Mo 1.0 415/16/1 30 Mo 1.0 415/7/1 20 Mo 1.0415/17/1 30 Mo 1.0 415/3/1 8 ZnO 1.0 415/4/1 15 Mo 1.0 350/1.25/5 30

What is claimed is:
 1. A method of forming a non-polarizing region in apolarizing glass comprising the steps of: a) providing a glass having apolarizing layer, said polarizing layer comprising elongated particles;and, b) selectively subjecting a region of said polarizing layer to athermal heating treatment to respheroidize said elongated particles insaid region and thereby render said glass in said region non-polarizing.2. The method of claim 1, wherein said elongated particles are selectedfrom the group consisting of AgCl_(x)Br_(1−x), CuCl_(x)Br_(1−x), where xhas a value between 0 and 1, Pb-borate, AgI, CuI and Cu/Cd halides. 3.The method of claim 1, wherein said thermal heating is conducted at atemperature of at least 450° C.
 4. The method of claim 3, wherein saidthermal heating is conducted at a temperature of at least 500° C.
 5. Themethod of claim 1, wherein said thermal heating is achieved bycontacting said region with a heating source selected from the groupconsisting of a laser, electron beam, and ion beam.
 6. A glass having apattern of polarizing and non-polarizing regions formed according to theprocess of claim 1.